This invention relates to a method of creating at least one set of machining parameters referred to herein as a "machining condition series" for use in a machine tools such as a discharge machining systems
Conventionally, the machining conditions for operating the machine tool are determined on the basis of required workplece specifications and the machine operator's experience and knowledge. For example, in discharge machining, the machine operator determines the machining condition series on the basis of finished surface roughness, shape characteristics and the like of the workpiece, and inputs the data to the machine tool. In discharge machining and other types of machining generally, phased processes from roughing to finishing are used to obtain the required roughness and improve the machining speed. Planning for changing the machining conditions is carried out on the basis of the operator's knowledge.
When the machine tool is operated, the experience and knowledge of a skilled operator is indispensable in determining the machining conditions and the machining condition series. However, through rapid progress in data processing technology, as described in Japanese Patent Laid-Open No. 62-130130 and Japanese Patent Laid-open No. 62-130131, there has been achieved an apparatus for creating a machining condition series which automatically calculates the machining conditions on the basis of data on the machining electrode and the workpiece.
FIG. 5 is a block diagram outlining a conventional method of creating a machining condition series. In FIG. 5, reference numeral 1 designates an input section for operator input of parameters such as the machining base area, machining depth, a finished surface roughness, electrode wear amount, etc., on the basis of the machining specifications of the workpiece. Further, reference numeral 2 designates a unit for generating a machining condition series which produces :he machining conditions and the machining condition series on the basis of machining characteristic data 4 and the inputted data from the input section 1. The machining characteristic data 4 includes data on the workpiece.
The operation of the above conventional method is as follows:
When the operator inputs machining base area, machining depth, finished surface roughness, electrode wear amount, etc., on the basis of the machining specifications of the workpiece, the unit 2 produces the machining conditions and the machining condition series on the basis of the inputted data from the input section 1 and the machining characteristic data 4 prepared in advance. Moreover, the machining condition series is displayed in the same state as the form being inputted to the machining tool, or eg., is printed out. Additionally, a plurality of the machining condition series are indicated together with the respective estimated times for machining, and the indicated data may be selected by the operator.
In general, when high finishing precision is required, a machining speed rapidly slows down. For example, FIG. 6 is a graph indicating the relation between surface roughness--and machining speed, classified by wear rate of the electrode in discharge machining. In FIG. 6, when the finished surface roughness is decreased from 25 .mu.mR.sub.max to 12.5 .mu.mR.sub.max, the machining increases five to seven-fold. That is, increasing finished surface precision causes the machining time to be rapidly extended. Therefore, in order to reduce production cost and machining time, finished surface roughness as far as possible on the "rough" side while still obtaining satisfactory product.
The conventional method of creating a machining condition series comprising the above steps is disadvantageous in the following way. The machining specifications are indicated by absolute numerical values. Frequently, the production cost and machining time could both be lowered by a little moderation of the machining specifications, however, the operator can not recognize how to achieve this end.
Furthermore, workpiece precision has an inverse relation with and large influence on machining speed. However, in designing a workpiece detailed decisions on machining precision data, e.g., the finished surface roughness, are unusual, and the machining precision data are divided into classes having relationally wide ranges. Accordingly, in machining, the operator flexibly interprets the machining precision parameters into consideration the importance of the workpiece, the operating conditions, the delivery deadline and the like and makes a compromise between machining speed and machining precision. That is, when each machining specification is set at a singular value, it takes much time to find a suitable compromise between machining speed and machining precision.